On construction sites various types of measuring instruments are used for measuring distances and angles between objects. Several conventional measuring instruments, such as construction lasers or surveying instruments, use a laser light source for measuring a distance, for measuring a position of an object, for indicating a direction or indicating a plane in space.
Special measuring instruments, such as a grade laser, a levelling apparatus or laser levelling apparatus, which functions are usually included in a construction laser, measures, for example, with the aid of a leveling rule, differences in height and establishes height horizons. For example, a levelling apparatus comprises a targeting telescope which, using a level or a pendulum compensator, can be oriented perpendicular to the plumb line direction. In addition to the measurement of positions, particularly differences in height, horizontal planes or vertical planes or sloped planes can be established, for example by rotating a laser beam.
Different detectors based on the photo detection of the emitted laser light of the measuring instruments are known. For example, WO 2006/048007 A1 describes a light beam receiver for analyzing the reception of light beams by means of a plurality of light beam detector elements and integrators for light beam element-based signals as well as a light conducting rod. Other detectors include a positioning device for detecting light of a fan-shaped laser beam described in WO 2009/154625 A1.
On large construction sites multiple laser systems each comprising a laser device emitting laser light and a laser beam detector may be employed at the same time. Therefore, there is a problem that a detector may be hit by laser light of different laser devices, i.e. by a laser device which is actually not associated with the detector and may then be erroneously used as a reference.
Accordingly, there is a need that a detector is able to identify the laser device which emitted the light that the detector detects. In other words, it is desirable that the detector recognizes its partnering laser device, the pair forming a corresponding laser system.
Further, since potentially several laser systems of laser devices and detectors from the same manufacturer can be employed on the same construction site, it is desired to be able to differentiate between the laser systems and provide an individual characteristic, such as a “fingerprint”, for each system.